The present invention relates to methods of extruding and more particularly to a method for extruding an aluminum tube having a knurled outer surface.
Extruded tubes are well known in the art and the process for manufacturing such tubes, when made from aluminum, generally comprises heating aluminum logs or billets and, under the influence of pressure, generally provided by hydraulics, and high temperature, the aluminum material is extruded through a die in which the center of the tube is relatively smooth and the external surface of the tube may have a knurled contour.
It has been found, however, that tubes formed by such a method cannot be held to a high degree of accuracy in that the resulting outer diameter (OD) and inner diameter (ID) of the tubes and more particularly their straightness or camber may vary greater than the permitted tolerances. Thus, there is a high degree of rejection of the tubes formed by this process resulting in substantial reworking of the material. The time and cost involved in the reworking significantly increases the cost to produce acceptable parts.